Electrostatic separating apparatus



0d. a, 1939. H w, BARTLETT 2,174,681

ELECTROSTATIC SEPARATING APPARATUS Filed Dec. 5, 1957 IN VENTOR.

ATTORNEY.

21W wa UNITED STATES PATENT OFFICE" 2,174,681 ELECTROSTATIC SEPARATINGAPPARATUS Harold W. Bartlett, Berkeley,

Rosenberg Bros. & (20., a corporation of Caliio Califi, assignor to SanFrancisco, Calif rnia Application December 3, 1937, Serial No. 177,950

2 Claims.

This invention relates generally to apparatus for effecting separationbetween fractions of divided material, in accordance with diiferences inelectrical characteristics, such as diflerences in conductivity ordielectric value. More particularly the invention relates to apparatusof the type making use 01' an electrostatic field, created by electricalcharges impressed upon spaced electrodes, and between which the materialis caused to pass, in efiecting a separation.

Apparatus of the above character have been known for many years, buttheir commercial applications have been limited. Use of a high potentialelectrostatic field for the removal of dust particles from air, as forexample for removing smoke from flue gases, has achieved considerablecommercial success. .However, at-- tempts to apply somewhat the sameprinciples to separation between fractions of solid materials, have notmet with commercial success. I attribute this largely to the manner inwhich the materials have been subjected to the-electrostatic field, andto the absence of a proper arrangement whereby the separating actioncould be stabilized and made uniform.

It is an object of the present invention to provide an apparatus whichcan be successfully applied in many industries,.to separate fractions ofsolid material having different electrical characteristics, as forexample differences in conductivity, dielectric strength or both. Inattaining this object I have provided an arrangement whereby thematerial being subjected to the electrostatic field is dropped in freefalling fashion through a separating zone, and whereby the electrodesare fso arranged and are of such a character as to produce acomparatively constant electrostatic separating action.

Further objects of the invention will appear from the followingdescription in which the preferred embodiment of the-invention has beenexplained in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Fig. 1 is a side elevational view, illustrating in diagrammatic fashion,apparatus incorporating the present invention.

Fig. 2 is a cross-sectional detail taken along the line 2-2 of Fig. 1.

Fig. 3 is a schematic circuit diagram, to facilitate an understanding ofthe invention, and to show 'the manner in which the electrodes areconnected to a source of high unidirectional potential. v

The apparatus comprising the present inven- (c1. zo9 130) tion makes useof an arrangement of electrodes, source of unidirectional The electrodesare adapted to laterally directed electronic wind through a zone ofseparation. Suitable conveying means serves to drop thematerial to beseparated into the zone of separation, where it is acted upon by theelectronic wind, to eifect a separation in accordance with difierencesin electrical characteristics. Below the zone of 10 separation suitablecollecting means is provided, as for example bins or receptacles intowhich the two or more separated fractions fall.

Referring to the drawing I have shown generally upright electrodes Illand il,which are disposed upon opposite sides of a separation zone A.Electrode Ill may .vary 8.5110 structural details, but in this instanceit is formed of wire screening, with the metal points l2 extending fromone side of the same. Any suitable mounting can be provided to supportthis electrode, as for example the high tension insulators l3, and frameIt.

Electrode ll may also vary as to details, but in this instance it islikewise a wire screen. The *2 foraminated nature of such a screenappears to facilitate maintenance of the desired ionic wind. Whileelectrode 1 I may be stationary in the same manner as electrode in, itis desirable in the handling of certain materials, to form highpotential. create a i the screen as an endless belt, carried by theinsulated pulleys or rollers I 6, l1 and I8. At one point the belt isshown being engaged by a rotary cleaning brush l9. When in operation oneof the rollers supporting the electrode II, as for example roller i1. isrotated at a slow speed from a suitable source of power, and the brushis is likewise driven to remove any particles adhering to the electrode.A terminal 2| is shown for making electrical connections with theelectrode l0, and likewise suitable provision is made for makingelectrical connections with electrode I I as for example .a contactingroller 22, which connects with the terminal 23.

Assuming that oppositely directed potentials are placed upon theelectrodes l0 and H, electrode lli creates the effect of so-calledelectronic wind in a direction laterally across the separating space A.-One might expect the plane of neutral potential of the electrostaticfield between electrodes l0 and II, to be about midway between theseelectrodes. However, tests have shown that without supplemental means aswill be presently described, the neutral plane appears to be shifted toa position in proximity symmetrical field has been found to seriouslyinterfere with uniformity of separating action.

The meanswhich I utilize to stabilize the electrostaticfield, and toshift the neutral plane to a region substantially mid-way between theelectrodes l0 and H, makesuse of a neutralizing electrode 24. Thiselectrode can be'formed of wire screening, with its one side providedwith the metal points 26. It is shown carried by a suitable supportmeans, such as the insulators 21 and supporting frame 28. A suitableterminal 29 is provided for making connection to the high potentialenergizing system. To facilitate making adjustments, frame 28 can haveadjustable connections 3i, with the main support frame 32,

The means for supplying material to the separating zone A, can consistof suitable conveying means, such as a shaker conveyor 33. The dischargeend of this conveyor is disposed above the separating zone A, so that asmaterial drops from the end of the conveyor, it progresses do nwardly infree falling fashion, substantially as a sheet. Below the separatingzone A a plurality of separate receivers 34, 35 and 36 are provided.These receivers may...connect with the associated conveying conduits 38,39 and 40.

The manner in which electrical connections are made can be bestexplained by reference to Fig. 3. A high potential transformer 42 isconnected with some suitable source of alternating current, and the highpotential secondary of this transformer connects with a rectifier 43.Leads L1 and L2, from the high potential'secondary side 'of rectifier43, connect respectively to the electrode Ill, and to the electrodes IIand 24. Recti-- fier 43 can be of the electronic type, 'afiording aunidirectional pulsating output. A mechanical commutating type ofrectifier can also be used, in which case the unidirectional outputpulsates with a substantially flat topped wave form. With the electrodel0 measuring in the neighborhood of 1,500 square inches, and electrodesl0 and H placed apart a distance in the neighborhood of 18 inches, apotential in the neighborhood of twenty thousand volts gave goodresults.

- In the past I have used the apparatus described above on various foodproducts, including raisins for the purpose of separating raisins fromleaf and stem material, unmilled rice for the purpose of separatingricefrom water cress seed,

and on shelled nuts like almonds for the purpose of separating the meatof the nut from shell material. In employing the apparatus describedabove, for the treatment of a material such as raisins, the raisins are'supplied'from conveyor 33, and permitted to drop in free fallingfashion down into the separating zone A. The raisins are deflected onlyslightly by the ionic wind created within the separating zone, but thestem and leaf material, because of a difference in dielectric value andconductivity, as compared to the raisins, are deflected to aconsiderable extent so that below the separating zone, the raisins fallin one collecting receiver, while the stem and looseleaf material fallinto one or more separate receptacles. In the treatment of unmilled riceit is desirable to first pass the rice through a suitable machine forremoving the beards from r with one 'of the electrodes. The resultingnonthe rice kernels, after which the rice is likewise supplied by theconveyor 33, and permitted to drop down through the separating zone. Thewater cress seed is deflected laterally by the ionic wind to an extentsubstantially greater than the rice kernels, so that the rice kernelsfall in one receptacle, while the seeds fall in another receptacle.Substantially the same separating action is exerted upon shelled nutssuch as almonds, in which case the shell material or fragments of thehull are deflected to a greater extent than the meat of the nut.

In the handling of materials as described above, small light material,such as pieces of stem or leaf material, or beards from rice, may adhereto electrode H, and tend to set up a counter electronic wind. It is forthis reason that electrode II is preferably in the form of an endlessbelt, whereby such material is continuously removed by the brush l9. .s

The particular manner described above for constructing the electrodeIll, is relatively simple and effective. However, in place of suchelectrode, I have used relatively fine wires stretched parallel abouttwo inches apart, and without the metal points 12. Such fine wires seemto have the ability of creating a laterally directed ionic wind.

In certain of my operations the conveyor 33' has been made of metal andgrounded. In other instances I have electrically connected. conveyor 33,to one side of the high potential supply, particulariy the side to whichelectrode I0 is connected. This serves to impart an initial charge tothe material as it falls from the conveyor 33, thereby augmenting theelectrostatic forces tending to displace the material laterally.

I claim:

1. .In apparatus for separating divided material in accordance withdifferences in electrical characteristics, means for maintainingan'ionic wind through a zone of electrostatic separation, said meansincluding an electrode at one side of said zone and adapted to induce anionic wind away from the same and through said zone, a foraminatedelectrode at the other side of said zone, and a third electrode behindsaid foraminated electrode and equipped with conducting points directedtowards the second electrode, and means for causing material to beseparated to pass through said separating zone.

2. In apparatus for separating divided material in accordance withdiiferences in electrical characteristics, means formaintaining an ionicwind through a zone of electrostatic separation, said means including apair of electrodes disposed on opposite sides of said zone and adaptedto be charged with oppositely directed electrical potentials, one ofsaid electrodes being provided with conducting points directed towardssaid zone and the other of said electrodes being foraminated, and aneutralizing electrode behind said foraminated electrode, whereby theneutral region of said zone is shifted to a region substantially mid-waybetween said first-named electrodes, said neutralizing electrode beinglikewise provided with conducting points directed towards saidseparating zone, and means for supplying material to be separated tosaid zone.

HAROID W. BARTLETI.

